The present invention relates to a power generation system capable of starting up in stand-alone operation and a control method for the power generation system.
In a micro gas turbine system described in a document: Isamu Inoue “UPS Function Built-in Micro-turbine Power Generation System” Meiden Jiho 2002, No. 2, pages 14-17, a plurality of unit micro gas turbine systems are started up in stand-alone operation, independently of a power system for supplying electric power to the micro gas turbine system.
For the stand-alone startup operation, each of the unit micro gas turbine systems is equipped with a power converter system including a storage battery. When power supply to the load is started after outage of the power system, the unit micro gas turbine systems are stopped once and then restarted.
In the above technique allowing the micro gas turbine system start up in stand-alone operation independently of the power system, each unit micro gas turbine system is connected with a storage battery system in parallel at the output end. The DC power from the storage battery is converted by the power converter system to AC power to serve in place of the power system, by which the electric power for starting up the micro gas turbine system is supplied.
In the above micro gas turbine system, a plurality of unit power generation systems, each of which is formed of a combination of a micro turbine system and a power converter for a storage battery, are connected together, allowing all the unit power generation systems to be started up simultaneously. However, each unit power generation system has to be equipped with a storage battery and that drives up the cost of the whole system.
Further, the above technique once stops the unit micro gas turbine systems when the operation mode of the micro gas turbine system is switched to stand-alone operation due to the outage of power system. Thus, the unit micro gas turbine systems can not be restarted quickly and it takes long to supply sufficient electric power to the load since the start of the stand-alone operation. Moreover, each storage battery is required to have a considerably large capacity since the electric power has to be supplied from the storage batteries to the load until the unit micro gas turbines are restarted.
The control mode of the power converter provided with the storage battery remains under AC voltage control until the total output power (total power generation) of unit micro gas turbine systems exceeds power consumption of the load. When the total output power of unit micro gas turbine systems exceeds the load power consumption, the control mode of the power converter including the storage battery shifts to current control. In this case, the balance of electric power for keeping a proper voltage level is maintained only by the current control of the storage batteries and output power control of the unit micro gas turbines, being susceptible to voltage fluctuation caused by variations in the load.